Well, the term 'message box or whatever' isn't really very helpful. Mostly the term 'message box' refers to the chat rooms PM box where people can post messages, but i'm sure thats not what you're referring to.
I just tested this with a CC email and it kept the email in tact and gave me the message 'The following users were not found:' And gave the misspelled name. Giving me a chance to fix the name. So i'm not sure what 'message box or whatever' you're referring to.
When typing peoples names for CC email, it does have an autofill option, its just a bit slow sometimes. Type in the first few letters of the name of the person you're sending to and it will show their name, and perhaps others with similar starting letters. You can select the right one and it fills in the rest.